THE CENTRAL NERVOUS SYSTEM 



769 



whole of the postero-external column in the sections immediately 

 above the highest of the divided roots will be found occupied by 

 degenerated fibres, while Coil's column may be free from de- 

 generation, or degenerated only at its outer border. Higher up 

 degeneration will be found to have involved the whole of the 

 postero-median column, and to have cleared away altogether 

 from the postero-external. The degeneration in the column of 

 Goll may be traced along the whole length of the cord to the 

 medulla, although the number of degenerated fibres diminishes 

 as we pass upward. The explanation of these appearances is as 



FIG. 319. POSTERIOR ROOTS FIG. 320. BRANCHING OF Pos- 



ENTERING SPINAL CORD (AT THE TERIOR ROOT-FIBRES IN CORD 



LEFT OF THE FIGURE). (DONALDSON, AFTER CAJAL). 



(From a preparation stained with Collaterals, Col, are seen coming 



aniline blue-black.) off from the two main branches of 



the root-fibres, DR, and ending 

 in arborizations. CC, cells in the 

 grey matter of the cord, whose 

 axons also give off collaterals. 



follows : It may be seen in preparations of the cord impregnated 

 by Golgi's method that the fibres of the posterior roots soon after 

 their entrance into the cord divide into two processes, one of 

 which runs up and the other down in the posterior column, or 

 in the adjoining portion of the posterior horn. From both of 

 these collaterals are given off at intervals to the grey matter. 

 The descending branches run downwards only for a short 

 distance, and the degeneration in the comma tract seen after 

 section of the cord is due to the division of these branches. 

 Many of the ascending branches pass up for a short distance in 



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